緩存池的作用就是減少重復(fù)創(chuàng)建資源,不是到每次需要使用資源再創(chuàng)建,而是提前準備好資源,每次需要時,從池中獲取,用完歸還.

我們看看下面簡單的 Hello World

從流中讀取字符串,每次都需要創(chuàng)建StringBuffer

import java.io.Reader; 
import java.io.IOException; 
 
public class ReaderUtil { 
    public ReaderUtil() { 
    } 

    /** 
     * Dumps the contents of the {@link Reader} to a 
     * String, closing the {@link Reader} when done. 
     */ 
    public String readToString(Reader in) throws IOException { 
        StringBuffer buf = new StringBuffer(); 
        try { 
            for(int c = in.read(); c != -1; c = in.read()) { 
                buf.append((char)c); 
            } 
            return buf.toString(); 
        } catch(IOException e) { 
            throw e; 
        } finally { 
            try { 
                in.close(); 
            } catch(Exception e) { 
                // ignored 
            } 
        } 
    } 
}

有些麻煩吧,我們使用緩存池獲取StringBuffer試試,直接上代碼

import java.io.IOException;
import java.io.Reader;
import org.apache.commons.pool2.ObjectPool;

public class ReaderUtil {
    
    private ObjectPool<StringBuffer> pool;
    
    public ReaderUtil(ObjectPool<StringBuffer> pool) {
        this.pool = pool;
    }

    /**
     * Dumps the contents of the {@link Reader} to a String, closing the {@link Reader} when done.
     */
    public String readToString(Reader in)
        throws IOException {
        StringBuffer buf = null;
        try {
            //通過緩存池獲取
            buf = pool.borrowObject();
            for (int c = in.read(); c != -1; c = in.read()) {
                buf.append((char) c);
            }
            return buf.toString();
        } catch (IOException e) {
            throw e;
        } catch (Exception e) {
            throw new RuntimeException("Unable to borrow buffer from pool" + e.toString());
        } finally {
            try {
                in.close();
            } catch (Exception e) {
                // ignored
            }
            try {
                if (null != buf) {
                    //使用完歸還回緩存池
                    pool.returnObject(buf);
                }
            } catch (Exception e) {
                // ignored
            }
        }
    }
}

import org.apache.commons.pool2.BasePooledObjectFactory;
import org.apache.commons.pool2.PooledObject;
import org.apache.commons.pool2.impl.DefaultPooledObject;

public class StringBufferFactory
    extends BasePooledObjectFactory<StringBuffer> {

    //創(chuàng)建對象的方法
    @Override
    public StringBuffer create() {
        return new StringBuffer();
    }

    /**
     * Use the default PooledObject implementation.
     * 使用默認的池化對象DefaultPooledObject封裝StringBuffer,使之帶上狀態(tài)屬性
     */
    @Override
    public PooledObject<StringBuffer> wrap(StringBuffer buffer) {
        return new DefaultPooledObject<StringBuffer>(buffer);
    }

    /**
     * When an object is returned to the pool, clear the buffer.
     * 鈍化對象,下次之前可以再復(fù)用該對象
     */
    @Override
    public void passivateObject(PooledObject<StringBuffer> pooledObject) {
        pooledObject.getObject().setLength(0);
    }

    // for all other methods, the no-op implementation
    // in BasePooledObjectFactory will suffice
}

ReaderUtil readerUtil = new ReaderUtil(new GenericObjectPool<StringBuffer>(new StringBufferFactory()));

代碼很簡單,下回代碼源碼解讀.